HVAC System Design 2 — Questions and Answers
Question 1: What is the primary purpose of a Manual J calculation in HVAC system design?
- Determine duct sizing requirements
- Calculate heating and cooling loads for a building (Correct answer)
- Size the refrigerant piping
- Establish ventilation airflow rates
Correct answer: Calculate heating and cooling loads for a building
Manual J is the ACCA standard method for calculating residential heating and cooling loads to properly size HVAC equipment.
Question 2: In a forced-air system, what is the recommended maximum air velocity in main supply ducts to minimize noise?
- 400–600 FPM
- 700–900 FPM (Correct answer)
- 1,000–1,200 FPM
- 1,500–2,000 FPM
Correct answer: 700–900 FPM
Main supply ducts are typically designed for 700–900 FPM to balance noise control with efficient air delivery.
Question 3: Which HVAC system configuration uses a single outdoor unit connected to multiple indoor fan-coil units?
- Chilled water system
- Variable refrigerant flow (VRF) system (Correct answer)
- Packaged rooftop unit
- Two-pipe hydronic system
Correct answer: Variable refrigerant flow (VRF) system
VRF systems use one outdoor condensing unit connected via refrigerant piping to multiple indoor fan-coil units for zone-level control.
Question 4: What does ACCA Manual D govern in HVAC system design?
- Equipment selection and sizing
- Residential duct design (Correct answer)
- Commercial ventilation requirements
- Refrigerant charge procedures
Correct answer: Residential duct design
Manual D is the ACCA standard for designing residential duct systems, covering duct sizing, layout, and airflow distribution.
Question 5: A building has a sensible heat ratio (SHR) of 0.70. This means:
- 70% of the cooling load is latent heat
- 70% of the cooling load is sensible heat (Correct answer)
- The system efficiency is 70%
- 30% of air supply is recirculated
Correct answer: 70% of the cooling load is sensible heat
SHR is the ratio of sensible cooling load to total cooling load, so an SHR of 0.70 means 70% of the load is sensible.
Question 6: In hydronic system design, what is the purpose of an expansion tank?
- Increase system water pressure
- Absorb volume changes as water heats and expands (Correct answer)
- Separate air from the circulating water
- Regulate flow to individual zones
Correct answer: Absorb volume changes as water heats and expands
An expansion tank accommodates the increase in water volume as it is heated, preventing excessive pressure buildup in a closed hydronic loop.
Question 7: What is the design dry-bulb outdoor temperature used for in HVAC load calculations?
- Sizing humidification equipment
- Determining the heating or cooling design load (Correct answer)
- Calculating duct insulation thickness
- Setting thermostat setpoints
Correct answer: Determining the heating or cooling design load
The outdoor design dry-bulb temperature (from ASHRAE tables) represents worst-case conditions used to calculate peak heating or cooling loads.
HVAC System Design 2
What is the primary purpose of a Manual J calculation in HVAC system design?